1. Field of the Invention
The invention in general is directed to a method for treating the distillation residue from the production of dialkyl and diaryl (substituted and unsubstituted) phosphorochloridothionates.
2. Prior Art
Phosphorochloridothionates are compounds of the structure: ##STR1## where R' and R" are the same or independently selected hydrocarbon radicals having 1-8 carbon atoms such as alkyl, aryl, alkaryl and cycloalkyl radicals.
In particular, the invention is directed to a method of treating the distillation residue from the production of dimethyl or diethyl phosphorochloridothionate.
The distillation residue formed when phosphorochloridothionates are produced, as is produced by the method disclosed in U.S. Pat. No. 3,089,890 incorporated herein by reference, is essentially comprised of a plastic mass of undissolved sulfur, other undissolved compounds and dissolved organophosphorous compounds. The distillation residue, which can be disposed of by hydrolysis on a batch basis has a highly offensive odor and is, in addition, thermally unstable. Storage of the distillation residue for any appreciable time has not been possible, as it generates problems associated with the handling of a thermally unstable, tarry mass. This problem is especially critical when diethyl phosphorochloridothionate is produced.
Presently when diethyl phosphorochloridothionate is prepared on a batch basis, the distillation residue resulting therefrom is decomposed by draining it into cold agitated water in a hydrolyzer, and heating the mixture slowly to a temperature of from 90.degree.-120.degree. C. By this process decomposition gases are produced at very uneven rates. During the peak rates of gas production, the odorous decomposition gases produced require the use of large volumes of air and fuel to prevent the odorous gases from escaping from the air swept hydrolyzers and abatement facilities into the atmosphere causing severe odor problems and concomitant hazardous working environment. The decomposition gases so produced, e.g. HCl, C.sub.2 H.sub.5 OH, C.sub.2 H.sub.5 SH, H.sub.2 S, C.sub.2 H.sub.5 Cl, CS.sub.2, C.sub.2 H.sub.5 S.sub.X C.sub.2 H.sub.5, are then burnt in an incinerator at from about 750.degree. C.-800.degree. C. This prior art method of treating the distillation residue results in high fuel consumption, and therefore, high fuel cost because of the large volumes of air which must be pumped through the hydrolyzers and the incinerators.
German Patent Application No. P 2617812, filed Apr. 23, 1976 discloses a method for treating the residue from the production of dialkyl thiophosphoric acid chloride. The method comprises, placing the residue in alkalized water, having a temperature of about -10.degree. C. to about 50.degree. C. and a pH of at least 10 in the resulting mixture, and contacting the aqueous phase and/or solid phases of the mixture formed therein with nitric acid at an elevated temperature and at a pH of below 3, to convert the residue into fertilizer and/or crystalline sulfur.
Currently, there is no disclosed method for storing the thermally unstable distillation residue in a form which will allow for its subsequent hydrolysis in controlled amount, or for continuously or semi-continuously hydrolyzing the residue immediately after it is produced. Presently, during the production of phosphorochloridothionates by the batch process, the thermally unstable distillation residue is transferred during the process into a product still and from there the plastic mass is transferred to a hydrolyzer and immediately hydrolyzed in the manner detailed above, or it is maintained in the product still at a temperature of about 70.degree. C. for subsequent hydrolysis. No means, therefore, is provided for controlling the amounts of the plastic mass being hydrolyzed at any specific time.